Apparently this is based on a leaked internal PC build of Gears of War 3 Epic made to test porting Unreal Engine 3 code to PC. (There also exists a PS3 build that you can find online.) The build was unfinished, so there's no campaign included, but all of Gears of War 3's multiplayer content is here: Versus, Horde and Beast Mode.
They've also added content from every other Gears of War game, mainly maps, weapons and characters from Gears of War Judgment, as well as some OC stuff. There's 91 characters and heaps of weapon skins to unlock with in-game achievements 
Having messed around with it today, what surprises me most is how professional it all feels. The control options on mouse and keyboard alone are way better than what Gears of War Reloaded, the 40 dollar re-release of Gears of War Ultimate from August, provided 
With all the added content it reminds me of when 343 Industries started adding cut and new content to the Halo games in the Master Chief Collection and serves as a glimpse into an alternate reality where Microsoft had two brain cells and made a similar collection for Gears of War
Anyway, I'm sure this news was useful to the 1 or 2 other people on Hexbear who care about these dumb games. To that person: you're welcome 
Edit: Also, the project somehow uses Steam to handle multiplayer, so you're playing with your Steam account. I hope Gaben doesn't ban my ass
They do have Paduk from Judgment and a male UIR soldier, at least